High dynamic range receiver front-end with q-enhancement

ABSTRACT

A preselect circuit maintains the dynamic range of a received RF input signal during bandpass filtering of the received RF input signal. The preselect circuit includes a Q-deficient passive bandpass filter for coupling to an antenna to receive a received RF input signal. The preselect circuit further includes a Q-enhancement circuit coupled to the Q-deficient passive bandpass filter, wherein the Q-enhancement circuit increases a Q-value of the Q-deficient passive bandpass filter by compensating for resistive inductive losses in the bandpass filter.

BACKGROUND

1. Field

This disclosure relates generally to wireless communication devices, andmore specifically to improving the dynamic range on the input of areceiver.

2. Background

Communication receivers receive both desirable and undesirable signalson their inputs. Signal selection filters for a receiver's “front-end”,such as preselect filters, have been designed for passing the desiredsignals relatively unfiltered and attenuating the undesired signals. Theeffectiveness of signal selection by a preselector is determined by theQ-value of a preselector's passband filter. Generally larger componentsin a passband filter may provide an adequate Q-value for providing thedesired passband filtering. Conventionally, if the Q-value wasinadequate, then larger, higher Q-value components were substituteduntil the preselector's passband filter provided adequate signalrejection.

As communication receivers became portable and mobile, variouscomponents in the receiver, including the receiver's front-end, havebeen integrated. Design tradeoffs exist between integration of receiverfront-end components, such as passband filters, and the reduction in theeffectiveness or quality of signal selection and rejection based uponthe reduction of the Q-value of the filter components.

While it is desirable to further integrate the components of a receiver,attempts to further integrate bandpass filters results in inferiorperformance of the system. System requirements of narrow bandwidths, lowdistortion and the need for low-power consumption run counter toconventional integration approaches.

Further integration attempts have placed buffer components at thebeginning of the receiver front-end resulting in a reduction of thedynamic range of the receiver front-end since buffer components includeactive devices which operate linearly only over a defined input signaldynamic range. Accordingly, when an RF input signal received at thereceiver front-end includes undesired signals (jammer signals) ofunpredictable magnitudes, then the active devices on a receiver'sfront-end may saturate, generate intermodulation signals and othernon-linearities which may distort the desired input signal.

Larger off-chip circuit elements have allowed system requirements to beattained. However, larger-dimensioned circuit elements inhibitreductions in the overall dimensions of the device as well ascontributes to increased device costs. Integration attempts may reducethe overall circuit component dimensions, however, such designs includeshortcomings including difficulties achieving high operating frequencieswith narrow bandwidths (i.e., high Q values) and a fundamentallimitation on the dynamic range at high Q values.

Different receiver architectures (e.g., direct conversion or low IFdesigns) have attempted to overcome further integration shortcomings ofpassive components, however, the limitations on the dynamic range isprohibitive. For example, moving the channel select filtering tobaseband results in amplifiers (e.g., Low Noise Amplifiers (LNAs)) andmixer circuits processing the entire RF spectrum including jamming(blocking) signals, resulting in the generation of further spuriousresponses and further desensitizing the receiver.

Improvements to poor dynamic range are possible by undesirablyincreasing the current consumption of circuit elements. For portable ormobile receivers, improving the dynamic range by increasing powerconsumption is undesirable and impractical. As stated, a bandpass filterincludes passive elements (e.g., L/C, transmission lines, acousticresonators) which in a bulk manufacturing quantities and integratedimplementations results in very low Q-values for the bandpass filter.Accordingly, there is a need in the art for a receiver having a receiverfront-end that exhibits high dynamic range on its inputs.

SUMMARY

Embodiments disclosed herein address the above stated needs by providinga preselect circuit exhibiting a high dynamic range during bandpassfiltering. In one aspect of the disclosed embodiments, a preselectcircuit includes a Q-deficient passive bandpass filter for coupling toan antenna to receive a received RF input signal. The preselect circuitfurther includes a Q-enhancement circuit coupled to the Q-deficientpassive bandpass filter, wherein the Q-enhancement circuit increases aQ-value of the Q-deficient passive bandpass filter by compensating forresistive inductive losses in the bandpass filter.

In another aspect of the disclosed embodiments, a receiver includes apreselector and mixer coupled to the preselect to down-convert apreselect filtered RF input signal. The preselector includes aQ-deficient passive bandpass filter for coupling to an antenna toreceive a received RF input signal and a Q-enhancement circuit coupledto the Q-deficient passive bandpass filter. The Q-enhancement circuit isconfigured to increase a Q-value of the Q-deficient passive bandpassfilter by compensating for resistive inductive losses in the bandpassfilter.

In another aspect of the disclosed embodiments, a wireless communicationdevice includes an antenna and a receiver coupled to the antenna. Thereceiver includes a Q-deficient passive bandpass filter for coupling tothe antenna to receive a received RF input signal and a Q-enhancementcircuit coupled to the Q-deficient passive bandpass filter. TheQ-enhancement circuit is configured to increase a Q-value of theQ-deficient passive bandpass filter by compensating for resistiveinductive losses in the bandpass filter.

In another aspect of the disclosed embodiments, a method forpreselecting a received input signal includes receiving an RF inputsignal from an antenna and passively bandpass filtering the RF inputsignal in a Q-deficient passive bandpass filter prior to the RF inputsignal being subjected to any active circuit elements. The methodfurther includes enhancing a deficient Q-value of the Q-deficientpassive bandpass filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a communications system that supports anumber of users and is capable of implementing at least some aspects ofthe embodiments discussed herein.

FIG. 2 is a block diagram of a transmitter system and a receiver systemin a wireless communication system capable of implementing at least someaspects of the embodiments discussed herein.

FIG. 3 is a block diagram illustrating an RF section of a wirelesscommunication device including a preselector capable of implementing atleast some aspects of the embodiments discussed herein.

FIG. 4 is a circuit diagram illustrating a preselector including anactive element at the input.

FIG. 5 is a circuit diagram illustrating a preselector including passiveelements at an input capable of implementing at least some aspects ofthe embodiments discussed herein.

FIG. 6 is a flow diagram illustrating a method for receiving an inputsignal capable of implementing at least some aspects of the embodimentsdiscussed herein.

DETAILED DESCRIPTION

Various embodiments are now described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of one or more embodiments. It may be evident, however,that such embodiment(s) may be practiced without these specific details.In other instances, well-known structures and devices are shown in blockdiagram form in order to facilitate describing one or more embodiments.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

Note that the exemplary embodiment is provided as an exemplar throughoutthis discussion, however, alternate embodiments may incorporate variousaspects without departing from the scope of the present embodiments.Specifically, one embodiment is applicable to a data processing system,a wireless communication system, a mobile IP network and any othersystem desiring to receive and process a wireless signal.

Circuits and devices described herein may operate in wirelesscommunication systems. Wireless communication systems are widelydeployed to provide various types of communication such as voice, data,and so on. These systems may be based on Code Division-Multiple Access(CDMA), Time Division-Multiple Access (TDMA), or some other modulationtechniques. A CDMA system provides certain advantages over other typesof systems, including increased system capacity.

A wireless communication system, including the circuits and devicesdescribed herein, may be designed to support one or more standards suchas the “TIA/EIA/IS-95-B Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System”referred to herein as the IS-95 standard, the standard offered by aconsortium named “3rd Generation Partnership Project” referred to hereinas 3GPP, and embodied in a set of documents including Document Nos. 3GPPTS 25.211, 3GPP TS 25.212, 3GPP TS 25.213, and 3GPP TS 25.214, 3GPP TS25.302, referred to herein as the W-CDMA standard, the standard offeredby a consortium named “3rd Generation Partnership Project 2” referred toherein as 3GPP2, and TR-45.5 referred to herein as the cdma2000standard, formerly called IS-2000 MC.

The circuits, devices, systems and methods described herein may be usedwith High Data Rate (HDR) communication systems. An HDR communicationsystem may be designed to conform to one or more standards such as the“cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2C.S0024-A, Version 1, March 2004, promulgated by the consortium “3rdGeneration Partnership Project 2.” The contents of the aforementionedstandard are incorporated by reference herein.

An HDR subscriber station, which may be referred to herein as an AccessTerminal (AT), may be mobile or stationary, and may communicate with oneor more HDR base stations, which may be referred to herein as Modem PoolTransceivers (MPTs). An access terminal transmits and receives datapackets through one or more modem pool transceivers to an HDR basestation controller, which may be referred to herein as a Modem PoolController (MPC). Modem pool transceivers and modem pool controllers areparts of a network called an access network. An access networktransports data packets between multiple access terminals. The accessnetwork may be further connected to additional networks outside theaccess network, such as a corporate intranet or the Internet, and maytransport data packets between each access terminal and such outsidenetworks. An access terminal may be any data device that communicatesthrough a wireless channel or through a wired channel, for example usingfiber optic or coaxial cables. An access terminal may further be any ofa number of types of devices including but not limited to PC card,compact flash, external or internal modem, or wireless or landlinephone. The communication channel through which the access terminal sendssignals to the modem pool transceiver is called a reverse channel. Thecommunication channel through which a modem pool transceiver sendssignals to an access terminal is called a forward channel.

FIG. 1 illustrates an example of a communications system 100 thatsupports a number of users and is capable of implementing at least someaspects of the embodiments discussed herein. Any of a variety ofalgorithms and methods may be used to schedule transmissions in system100. System 100 provides communication for a number of cells 102A-102G,each of which is serviced by a corresponding base station 104A-104G,respectively.

Wireless communication devices 106 in the coverage area may be fixed(i.e., stationary) or mobile. As shown in FIG. 1, various wirelesscommunication devices 106 are dispersed throughout the system. Eachwireless communication device 106 communicates with at least one andpossibly more base stations 104 on a forward link and a reverse link atany given moment depending on, for example, whether soft handoff isemployed or whether the terminal is designed and operated to(concurrently or sequentially) receive multiple transmissions frommultiple base stations.

The forward link refers to transmission from a base station 104 to awireless communication device 106, and the reverse link refers totransmission from a wireless communication device 106 to a base station104. In FIG. 1, base station 104A transmits data to wirelesscommunication devices 106A and 106J on a forward link; similarly basestation 104B transmits data to wireless communication devices 106B and106J, base station 104C transmits data to wireless communication device106C, and so on.

FIG. 2 is a block diagram of a transmitter system 210 and a receiversystem 250 in a wireless communication system 200. At transmitter system210, traffic data is sent (typically in packets that may be of variablelengths) from a data source 212 to a Transmit (TX) data processor 214.TX data processor 214 then formats and codes the traffic data to providecoded data. The coded data is then modulated (i.e., symbol mapped) basedon one or more modulation schemes (e.g., BPSK, QSPK, M-PSK, or M-QAM) toprovide modulation symbols (i.e., modulated data).

A Transmitter (TMTR) unit 216 then converts the modulated data into oneor more analog signals and further amplifies, filters, quadraturemodulates, and upconverts the analog signals to generate a modulatedsignal. The modulated signal is then transmitted via an antenna 218 andover a wireless communication link to one or more receiver systems.

At receiver system 250, the transmitted modulated signal is received byan antenna 252 and provided to a receiver (RCVR) 254. Within receiver254, the received signal is conditioned (e.g., filter, amplified,frequency downconverted, and quadrature downconverted) and theconditioned signal is further digitized to provide ADC samples. TheAnalog-to-Digital Converter (ADC) samples may further be digitallypre-processed within receiver 254 to provide data samples. Receiver 254includes a preselector, described below, in accordance with variousaspects of the embodiments described herein.

A Receive (RX) data processor 256 then receives and processes the datasamples to provide decoded data, which is an estimate of the transmitteddata. The processing by RX data processor 256 may include, for example,equalization, demodulation, deinterleaving, and decoding. The processingat RX data processor 256 is performed in a manner that is complementaryto the processing performed at TX data processor 214. The decoded datais then provided to a data sink 258.

A controller 260 directs the operation at the receiver system. A memoryunit 262 provides storage for program codes and data used by controller260 and possibly other units within the receiver system.

The signal processing described above supports transmissions of varioustypes of traffic data (e.g., voice, video, packet data, and so on) inone direction from the transmitter system to the receiver system. Abi-directional communication system supports two-way data transmission.The processing shown in FIG. 2 can represent the forward link (i.e.,downlink) processing in a CDMA system, in which case, transmitter system210 can represent a base station and receiver system 254 can represent aterminal. The signal processing for the reverse link (i.e., uplink) isnot shown in FIG. 2 for simplicity.

FIG. 3 is a block diagram of one aspect illustrating an exemplary RFsection of a wireless communication device 300 including the receivesystem 250 of FIG. 2. Wireless communication device 300 may be any of avariety of mobile or stationary devices with wireless capabilities, suchas a cellular radiotelephone, satellite phone, smart phone, personaldigital assistant (PDA), mobile or desktop computer, digital video oraudio device, gaming console, television console, a set top box, or anyother device equipped for wireless communication.

As shown in FIG. 3, device 300 includes an antenna 352 that transmitsand receives wireless RF signals. A duplexer 314 couples RX signals (RXSIGNAL) received by antenna 352 to a receiver 354, and couples TX outputsignals (TX SIGNAL) generated by a transmitter 318 to antenna 352. Inthe example of FIG. 3, receiver 354 includes preselector 320, low noiseamplifier (LNA) 333, mixer 324, local oscillator (LO) 326, and a filter330. Transmitter 318 includes a power amplifier 328 that amplifies an RFoutput signal to produce a TX RF signal for transmission via duplexer314 and antenna 352. Transmitter 318 also may include a modem,digital-to-analog converter, mixer and filter circuitry (not shown) tomodulate and filter the output signal, and up-convert the signal from abaseband to a transmit band.

In receiver 354, preselector 320 filters and amplifies the RX signal andis further described below. In receiver 354, LNA 322 amplifies the RXsignal. LNA 322 may be a differential amplifier producing differentialoutput signals. Mixer 324 may be a wideband mixer that multiplies theamplified, signal from preselector 320 with the RX LO frequency todown-convert the desired RX signal to baseband, thereby producing an RXbaseband signal. Filter 330 filters the RX baseband signal to reduce theTX leakage signal and thereby reduce undesirable distortion. Filter 330may provide further filtering (i.e., a notch frequency filter) at whichthe TX signal is strongly attenuated. Filter 330 may be configured suchthat the notch frequency generally corresponds to the offset frequencyof the down-converted TX leakage signal relative to the center frequency(e.g., 0 Hz) of the baseband. Filter 330 may also be configured tosubstantially reject frequencies outside the desired baseband. Receiver354 may further include an analog-to-digital converter and modem (notshown) to demodulate and decode the desired RX signal.

Antenna 352 may receive a RX signals (RX SIGNAL) including both adesired signal and a jammer signal, as shown in FIG. 3. Hence,preselector 320 may receive an RX signal including the desired signaland possibly the jammer signal, as well as the TX leakage signal coupledfrom the transmit path via duplexer 314. Preselector 320 filters andamplifies this combined RX signal to produce an amplified RF signal. TheTX leakage signal may produce second order distortion and crossmodulation distortion (XMD). The jammer signal is an undesired signalthat may correspond to a signal generated from a nearby source such as awireless transmission station. In some cases, a jammer signal may havean amplitude that is much higher than that of the desired signal and maybe located close in frequency to the desired signal. The TX leakagesignal also may have a large amplitude relative to the desired signalbecause the transmit signal produced by power amplifier 328 is oftenmuch larger in amplitude than the desired signal.

The TX leakage signal is outside the RX band. However, TX leakage signalstill may cause undesirable distortion. For example, any non-linearityin preselector 320 can cause the modulation of TX leakage signal to betransferred to the narrow-band jammer, resulting in a widened spectrumaround the jammer. This spectral widening is referred to as crossmodulation distortion (XMD). This XMD acts as additional noise thatdegrades the performance of the wireless communication device. Thisnoise degrades sensitivity so that the smallest desired signal that canbe reliably detected by receiver 354 needs to have a larger amplitude.XMD can also be generated in mixer 324.

In wideband receivers, the received RF signal (RX SIGNAL) may either bedownconverted from a wide frequency range to a lower intermediatefrequency (IF) using, for example, a super heterodyne receiver ordirectly downconverted to baseband accoruding to, for example, a ZeroIntermediate Frequency (ZIF) receiver. These receivers utilize apreselector 320 including a bandpass filter with a narrow bandwidth forpreselection requiring a high-Q filter. Unfortunately, active bandpassfilters may exhibit limited dynamic range or excessive current draw and,therefore, result in the inclusion of both desired RX signals andundesired received signals (e.g., jammer signals and TX leakage signal)in the RF amplification process.

FIG. 4 illustrates a preselector 400 including an initial activeelement. Preselector 400 includes in an active input buffer 404 forreceiving the RX signal (e.g., desired signal and any jammer signal) andthe TX leakage signal (also collectively referred to herein as the “RFinput signal 402”). The active input buffer 404 buffers and amplifiesthe RF input signal 402 to form an actively buffered RF input signal atnode A.

The actively buffered RF input signal is subjected to a passive bandpassfilter 406 including a capacitor C 408, an inductor L 410 including aresistive inductive loss illustrated as resistor Rp 412. In practicalimplementations of mobile or portable receivers, passive bandpassfilters, such as passive bandpass filter 406, are implemented accordingto mass-produced passive components such as capacitors and inductors ofreduced dimensions and tolerances. Reduced dimensions and tolerances ofbandpass filter components results in a Q-deficient passive bandpassfilter. A Q-deficient bandpass filter exhibits inadequate passbandselection and out-of-band rejection of the RF input signal and highloss.

Conventionally, the Q-value of passive bandpass filters could beadequately increased based upon selection of higher Q-value capacitorsand inductors or large resonate cavities, albeit of larger dimensions.However, in portable and mobile devices, the Q-value of a Q-deficientpassive bandpass filter 406 may be augmented by a Q-enhancement circuit414. In one aspect, the Q-enhancement circuit 414 is coupled in parallelto the resistive inductive loss resistor Rp 412 of the Q-deficientpassive bandpass filter 406. The Q-enhancement circuit 414 may beconfigured as a negative resistor for compensating for the resistiveinductive loss resistor Rp 412. The Q-enhancement circuit 414 may beimplemented as a transconductance active device as illustrated.

Preselector 400 may further include an output buffer 416 coupled to theQ-deficient passive bandpass filter 406 and the Q-enhancement circuit414. The output buffer 416 may provide impedance matching with the mixer324 of FIG. 3.

One of the shortcomings of preselector 400 includes the activeconfiguration of active input buffer 404. The active input buffer 404includes a transistor 418 which directly receives the unpredictablyfluctuating dynamic range (i.e., signal level magnitudes) of the RFinput signal. For example, a high signal level of the RF input signal,such as a jamming signal, frequently exceeds the dynamic range of thetransistor 418 resulting in saturation of transistor 418 causing thegeneration of distortion in the form of cross modulation distortion(XMD) discussed above. Accordingly, the active input buffer 404restricts the dynamic range of the preselector 400. While the dynamicrange of an active input buffer may be extended by providing excessivecurrent to the active transistor, excessive and unnecessary powerconsumption runs counter to the prudent power management design goalsfor portable and mobile devices. Accordingly, due to the broad dynamicrange requirements for a receiver 354 of FIG. 3, a high dynamic rangepreselector is desired.

FIG. 5 illustrates a preselector in accordance with various aspects ofthe disclosed embodiments. Accordingly, a preselector 500 includespassive bandpass filtering with an acceptably narrow bandwidthattainable without unduly restricting the dynamic range. The preselector500 receives an RF input signal 502 which is initially passed to aQ-deficient passive bandpass filter 504. The Q-deficient passivebandpass filter 504 is a resonator and may include different componentsinclude discrete inductors/capacitors, transmission lines, cavityresonators and acoustic resonators. The Q-deficient passive bandpassfilter 504 is illustrated to include a capacitor C 506, an inductor L508 including a resistive resonator loss illustrated as resistor Rp 510

The Q-deficient passive bandpass filter 504 includes only passiveelements which provide a high dynamic range for filtering the entire RFinput signal. Therefore, before the high dynamic range RF input signalencounters any active devices, it has already been filtered by theQ-deficient passive bandpass filter 504 which has rejected theout-of-band signals which would tend to exhibit the dynamic rangeextremes. The dynamic range is bounded by noise on the lower end of therange and by linearity of the devices on the upper end of the range.Passive devices such as passive capacitors and inductors introduceessentially no noise on the lower end of the dynamic range and do notbecome non-linear on the upper end of their dynamic range. In contrast,active devices, such as transistor 418 of FIG. 4, introduce noise on thelower end of their dynamic range and then saturates on the upper end ofthe dynamic range causing an introduction of non-linearities into the RFinput signals. Accordingly, active devices have a much smaller dynamicrange than passive devices and are therefore undesirable in receiverfront-ends for passing signals that have not been initially filteredinto the dynamic range of the active device.

Continuing reference to FIG. 5, the Q-deficient passive bandpass filter504 is configured at the input of preselector 500 to receive the RFinput signal prior to the RF input signal passing through any activedevices. Furthermore, the preselector 500 is configured at the input ofthe receiver 354 of FIG. 3 to receive the received RF input signal (RXsignal and TX leakage signal) prior to the RF input signal passingthrough any active devices. According to the various aspects of theembodiments disclosed herein, the RF input signal received at antenna352 of FIG. 3 first passes through the Q-deficient passive bandpassfilter 504 of FIG. 5 before passing through any active devices.

In operation, the received RF input signal (RX signal and TX leakagesignal) first couples to the passive preselect filtering of Q-deficientpassive bandpass filter 504 including the capacitor C 506 and theinductor L 508 before connection to any active device. Coupling thereceived RF input signal first to non-active circuitry results in alower power configuration since an active circuit receiving a receivedRF signal (RX signal) would require high power in order to exhibit alarge dynamic range. The Q-deficient passive bandpass filter 504provides filtering of at least a portion of unwanted signals (e.g.,jammer signals and TX leakage signal) thus reducing the dynamic rangerequirements of subsequent active devices in receiver 354 of FIG. 3.

It is noted that in mobile or portable devices including receivers, thereduction in physical dimensions of filter circuit components results ina reduction in the “Q-value” of the filter resulting from the filtercircuit components. Accordingly, realization of reduced-dimensionbandpass filters results in a reduction in the Q-value of the filters.As stated, one method for increasing the Q-value of a Q-deficientpassive bandpass filter is to mitigate the resistive losses in thepassive components of the passive bandpass filter by providing anegative resistance. Accordingly, preselector 500 further includes aQ-enhancement circuit 512 coupled in parallel to the resistive inductiveloss resistor Rp 510 of the Q-deficient passive bandpass filter 504. TheQ-enhancement circuit 512 may be configured as a negative resistor forcompensating for the resistive inductive loss resistor Rp 510. TheQ-enhancement circuit 512 may be implemented as a transconductanceactive device as illustrated in FIG. 5. Accordingly, the first activedevice through which the RF input signal passes is the active device inthe Q-enhancement circuit 412 and not an active device associated withan active input buffer such as active input buffer 404 of FIG. 4 whichincludes transistor 404.

The Q-enhancement circuit may be variously configured. In one aspect,Q-enhancement circuit 512 is configured as a negative resistance tocancel the effect of losses, such as resistive inductive lossillustrated as resistor Rp 510. Positive feedback from Q-enhancementcircuit 512 reduces the effect of losses in inductor loss resistance Rp510. The amount of positive feedback is controlled by the ratio ofcapacitors 526 and 528 with the Q-value being determined by the feedbackprovided by the capacitors 526 and 528 as well as the current followingthrough transistor 514. The losses of inductor 508 and capacitor 506 aremodeled by the inductor loss resistance Rp 510.

In one aspect, the Q-enhancement circuit 512 is configured as a negativeresistance circuit arranged in a Colpitts configuration. TheQ-enhancement circuit 512 includes a transistor 514 having a collectorcoupled to a power source 516 via resistor 518. Resistor 518 can bereplaced with an inductor. A first bias resistor 520 is coupled betweena power source 522 and the base of the transistor 514. A current source524 is coupled between the emitter of the transistor 514 and a groundpotential. A first feedback capacitor 526 is coupled between the baseand emitter of the transistor 514. A second feedback capacitor 528 iscoupled between the emitter of the transistor 514 and the groundpotential.

The preselector 500 may further include an impedance transformer 530used to decouple the incoming RF input signal from the antenna 352 ofFIG. 3. The impedance transformer 530 may be adjusted to match theelectrical load of the antenna-side of the preselector 500 in order tomaximize the power transfer and minimize reflections from the RF inputsignal, thus obtain the desired overall filter response.

FIG. 6 is a flow diagram illustrating a method for receiving an inputsignal capable of implementing at least some aspects of the embodimentsdiscussed herein. A process 600 illustrates maintaining a high-dynamicrange for a received RF input signal in a preselector circuit. In step602, an RF input signal is received from the antenna and may passthrough a duplexer 314 of FIG. 3 and an impedance transformer 530 ofFIG. 5. As stated, the received RF input signal may include high-dynamicrange signal levels on the RF input signals which would normally becomedistorted in a receiver front-end.

In a step 604, the received RF input signal is passively filtered in aQ-deficient bandpass filter. The Q-deficient passive bandpass filterincludes only passive elements which provide a high dynamic range forfiltering the entire RF input signal. Therefore, before the high dynamicrange RF input signal encounters any active devices, it has already beenfiltered by the Q-deficient passive bandpass filter which has rejectedthe out-of-band signals which would tend to exhibit the dynamic rangeextremes. Passive devices such as passive capacitors and inductorsintroduce essentially no noise on the lower end of the dynamic range anddo not become non-linear on the upper end of their dynamic range. Incontrast, active devices, introduce noise on the lower end of theirdynamic range and then saturates on the upper end of the dynamic rangecausing an introduction of non-linearities into the RF input signals.

In step 606, the Q-value of the Q-deficient bandpass filter is enhancedusing a Q-enhancement circuit. As stated, in mobile or portable devicesincluding receivers, the reduction in physical dimensions of filtercircuit components results in a reduction in the narrowness of thebandwidth or Q-value of the filter resulting from the filter circuitcomponents. Accordingly, realization of reduced-dimension bandpassfilters results in a reduction in the Q-value of the filters. TheQ-value is increased by mitigating the resistive losses in the passivecomponents of the passive bandpass filter by providing a negativeresistance. Accordingly, a Q-enhancement circuit is coupled in parallelto the resistive inductive loss resistor of the Q-deficient passivebandpass filter. Accordingly, the first active device through which theRF input signal passes is the active device in the Q-enhancement circuitand not an active device associated with an active input buffer.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present embodiments.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, for example, acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method, comprising: receiving an RF inputsignal from an antenna; passively bandpass filtering the RF input signalin a Q-deficient passive bandpass filter prior to the RF input signalbeing subjected to any active circuit elements; and enhancing adeficient Q-value of the Q-deficient passive bandpass filter.
 2. Themethod of claim 1, wherein the passively bandpass filtering the RF inputsignal further comprises maintaining a dynamic range of the RF inputsignal during the passively bandpass filtering.
 3. The method of claim1, further comprising impedance transforming the RF input signal priorto passively filtering the RF input signal.
 4. A circuit, comprising:means for receiving an RF input signal from an antenna; means forpassively bandpass filtering the RF input signal in a Q-deficientpassive bandpass filter prior to the RF input signal being subjected toany active circuit elements; and means for enhancing a deficient Q-valueof the Q-deficient passive bandpass filter.
 5. The method of claim 4,further comprising means for impedance transforming the RF input signalprior to passively filtering the RF input signal.